Hypercalcemia and hyperosteolysis in vitamin D intoxication: effects of clodronate therapy

The Potential Role of Vitamin D Supplementation in Cognitive Impairment Prevention

BACKGROUND

Vitamin D is implicated in many processes in the central nervous system (CNS), such as neurogenesis, neurotransmitter synthesis, synaptogenesis and protection against oxidative stress, thereby exerting a neuroprotective effect.

OBJECTIVE

In the present review, we aimed to evaluate the potential benefit(s) of vitamin D supplementation for CNS aging in different clinical contexts.

METHODS

We performed a literature search, looking for clinical trials and randomized clinical trials evaluating the effect of vitamin D supplementation on different endpoints related to cognitive outcomes.

RESULTS

Firstly, we identified 16 papers dealing with the impact of vitamin D supplementation on cognitive function in healthy subjects; the current literature suggests a real role for vitamin D supplementation in the prevention of cognitive decay in this clinical setting. Conversely, two papers suggest that vitamin D supplementation may be beneficial in patients with mild cognitive impairment (MCI). Finally, current data on vitamin D in Alzheimer's disease are contradictory.

CONCLUSION

Vitamin D supplementation may improve the cognitive outcomes of patients with MCI, whereas there is no evidence that it may prevent dementia or modulate the course of Alzheimer's disease.

Calcitriol induced hypercalcemia - a rare phenomenon in lung cancer: A case report

BACKGROUND

Calcitriol-induced hypercalcemia has been rarely reported in cases of lung cancer; however, it is frequently reported in cases of lymphoid malignancy and granulomatous disease. We present a rare case of hypercalcemia associated with squamous cell cancer of the lung with elevated calcitriol level.

CASE SUMMARY

A 61-year-old Caucasian female with severe hypercalcemia of 15 mg/dL, which led to a new diagnosis of metastatic lung cancer. Since the parathyroid hormone-related peptide (PTHrP) level was minimally elevated at 2.1 pmol/L, we believe excessive calcitriol production by tumor cells was the underlying mechanism for hypercalcemia. Calcitriol was significantly elevated at 130 pg/mL with a low 25-hydroxyvitamin D level of 25.9 ng/mL and suppressed PTH level of 8 pg/mL. Corticosteroids are generally used to treat calcitriol-induced hypercalcemia, but we successfully treated our patient with bisphosphonate, highlighting the further utility of bisphosphonates in hypercalcemia treatment.

CONCLUSION

We believe that the underlying cause of hypercalcemia, in this case of metastatic squamous cell lung carcinoma, was elevated calcitriol, which was likely produced by the tumor cells. In addition to PTHrP, calcitriol levels should be included in the workup for hypercalcemia in cases of lung cancer. However, the pathophysiology and prognostic significance of dysregulated calcitriol production in solid tumors remain unclear and warrant further research. Bisphosphonate may be used as a steroid-sparing therapy even in cases of calcitriol-induced hypercalcemia and warrants further investigation.

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

Role of vitamin D supplementation in the management of musculoskeletal diseases: update from an European Society of Clinical and Economical Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) working group

Vitamin D is a key component for optimal growth and for calcium-phosphate homeostasis. Skin photosynthesis is the main source of vitamin D. Limited sun exposure and insufficient dietary vitamin D supply justify vitamin D supplementation in certain age groups. In older adults, recommended doses for vitamin D supplementation vary between 200 and 2000 IU/day, to achieve a goal of circulating 25-hydroxyvitamin D (calcifediol) of at least 50 nmol/L. The target level depends on the population being supplemented, the assessed system, and the outcome. Several recent large randomized trials with oral vitamin D regimens varying between 2000 and 100,000 IU/month and mostly conducted in vitamin D-replete and healthy individuals have failed to detect any efficacy of these approaches for the prevention of fracture and falls. Considering the well-recognized major musculoskeletal disorders associated with severe vitamin D deficiency and taking into account a possible biphasic effects of vitamin D on fracture and fall risks, an European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) working group convened, carefully reviewed, and analyzed the meta-analyses of randomized controlled trials on the effects of vitamin D on fracture risk, falls or osteoarthritis, and came to the conclusion that 1000 IU daily should be recommended in patients at increased risk of vitamin D deficiency. The group also addressed the identification of patients possibly benefitting from a vitamin D loading dose to achieve early 25-hydroxyvitamin D therapeutic level or from calcifediol administration.

Impact of land use/land cover changes on water quality and human health in district Peshawar Pakistan

The quality and quantity of groundwater resources are affected by landuse/landcover (LULC) dynamics, particularly the increasing urbanization coupled with high household wastewater discharge and decreasing open lands. This study evaluates temporal changes of groundwater quality for 2012 and 2019, its relation to Landuse/landcover, and its impact on Peshawar's residents (study area), Pakistan. A total of 105 and 112 groundwater samples were collected from tube wells in 2012 and 2019. Samples were then analyzed for seven standard water quality parameters (i.e., pH, electric conductivity (EC), turbidity, chloride, calcium, magnesium, and nitrate). Patient data for waterborne diseases were also collected for the years 2012 and 2019 to relate the impact of groundwater quality on human health. Landsat satellite images were classified for the years 2012 and 2019 to observe landuse/landcover dynamics concerning groundwater quality. Results manifested a decrease in groundwater quality for the year 2019 compared to 2012 and were more highlighted in highly populated areas. The nitrate concentration level was found high in the vicinity of agricultural areas due to the excessive use of nitrogenous fertilizers and pesticides, and thus the methemoglobinemia patients ratio increased by 14% (48-62% for the year 2012 and 2019, respectively). Besides, Urinary Tract Infections, Peptic Ulcer, and Dental Caries diseases increased due to the high calcium and magnesium concentration. The overall results indicate that anthropogenic activities were the main driver of Spatio-temporal variability in groundwater quality of the study area. The study could help district health administration understand groundwater quality trends, make appropriate site-specific policies, and formulate future health regulations.

Vitamin D supplementation: upper limit for safety revisited?

Vitamin D overdosing includes hypercalcemia, hypercalciuria, and mineral deposits in soft tissues. A safety upper limit of 4000 IU/day, which is consistently accepted, has been challenged, since the risk of adverse events in other systems than calcium-phosphate homeostasis may depend not only on the dose, but on the outcome, the treatment regimen, and possibly the age, sex and vitamin D status. The therapeutic window of vitamin D supplementation may be narrower than hitherto recognized. The prevention and/or correction of vitamin D deficiency/insufficiency with 800–1000 IU/daily of vitamin D or 10 µg/day of calcifediol are safe. Because of their potential harm, larger doses given on the long term or in intermittent regimens should not be selected.

BISPHOSPHONATES FOR THE TREATMENT OF CALCITRIOL-INDUCED HYPERCALCEMIA

Objective

Calcitriol excess is a less common cause of hypercalcemia than hyperparathyroidism. Hypercalcemia due to calcitriol excess is usually managed acutely with intravenous (IV) fluid administration and dietary calcium restriction. Steroids and ketoconazole are second-line agents. There is evidence supporting the role of bone resorption in the genesis of hypercalcemia in vitamin D intoxication and for a rapid response of hypercalcemia to treatment with bisphosphonates. We seek to demonstrate the utility of bisphosphonates in calcitriol-induced hypercalcemia (CIH).

Methods

We present the case of a patient with recurrent CIH from a follicular lymphoma who achieved normalization and subsequent stabilization of serum calcium levels following bisphosphonate administration.

Results

A 77-year-old woman with a history of non-small cell lung cancer was admitted with dry mouth, polyuria, weight loss, and fatigue. She was found to have a calcium level of 14.7 mg/dL (normal range is 8.5 to 10.2 mg/dL), 25-hydroxyvitamin D of 47 ng/mL (normal range is 30 to 60 ng/mL), 1,25-dihydroxyvitamin D of 89 pg/mL (normal range is 18 to 72 pg/mL), and parathyroid hormone of 19 pg/mL (normal range is 15 to 65 pg/mL), which recurred despite treatment with IV fluids and strict low-calcium diet. She received 5 mg of IV zoledronic acid and normocalcemia was maintained thereafter, without any diagnosis-specific treatment for >3 months. Positron emission tomography with computed tomography eventually showed new innumerable foci of increased uptake in the skeleton and lymph node biopsy revealed grade 3A follicular lymphoma.

Conclusion

The first choice for CIH is treating the underlying cause. Bisphosphonates are, however, useful until a diagnosis is made, as they may be safer than steroids and can provide rapid relief even with a single treatment with minimal side effects.

Controversies in Vitamin D: Summary Statement From an International Conference

CONTEXT

Vitamin D is classically recognized as a regulator of calcium and phosphorus metabolism. Recent advances in the measurement of vitamin D metabolites, diagnosis of vitamin D deficiency, and clinical observations have led to an appreciation that along with its role in skeletal metabolism, vitamin D may well have an important role in nonclassical settings. Measurement of the circulating form of vitamin D that best describes total body stores, namely 25-hydroxyvitamin D, can be unreliable despite many sophisticated methodologies that have been proposed and implemented. Likewise, evidence from clinical studies showing a beneficial role of vitamin D in different disease states has been controversial and at times speculative. Moreover, the target concentrations of 25-hydroxyvitamin D to address a number of putative links between vitamin D inadequacy and nonskeletal diseases are further areas of uncertainty.

SETTING

To address these issues, an international conference on "Controversies in Vitamin D" was held in Pisa, Italy, in June 2017. Three main topics were addressed: (i) vitamin D assays and the definition of hypovitaminosis D; (ii) skeletal and extraskeletal effects of vitamin D; (iii) therapeutics of vitamin D.

RESULTS

This report provides a summary of the deliberations of the expert panels of the conference.

CONCLUSIONS

Despite great advances in our appreciation of vitamin D metabolism, measurements, biological actions on classical and nonclassical tissues, and therapeutics, all of which this report summarizes, much more work remains to be done so that our knowledge base can become even more secure.

Efficacy of a Standardized Oral Vitamin D Dosing Regimen in Nursing Home Residents

BACKGROUND

The prevalence of vitamin D deficiency in nursing home residents ranges from 79% to 98%.

OBJECTIVES

The aim of this cross-sectional observational study in somatic and psychogeriatric nursing home residents was to determine the efficacy of a standardized oral vitamin D dosing regimen (VDDR) consisting of a loading dose (LD) of cholecalciferol 200,000 IU followed by a maintenance dose (MD) of 100,000 IU every 13 weeks in obtaining and maintaining an adequate and safe vitamin D trough level (VDTL), defined as 75-220 nmol/L (reference range).

METHODS

Blood samples of nursing home residents who had received the LD followed by at least one MD were analyzed for VDTL, calcium, parathyroid hormone, and creatinine. Data on age, sex, race, body weight and height, co-morbidity, co-medication, number of MDs, calcium supplementation, smoking, and use of alcohol were obtained from patient charts. The primary outcome for the efficacy of the VDDR was the percentage of nursing home residents with a VDTL 75-220 nmol/L, with a target percentage of 85% for the dosing regimen to be considered efficacious.

RESULTS

In 91 (58%; 95% confidence interval [CI] 50-66) of 156 included nursing home residents, a VDTL within the reference range was measured (mean [standard deviation] 81 [28] nmol/L, range 13-150 nmol/L). The only variable that was identified as a significant risk indicator for obtaining a VDTL ≥ 75 nmol/L was the number of MDs being four or more (≥ 4 vs. < 4; odds ratio 2.7; 95% CI 1.4-5.3).

CONCLUSION

This standardized VDDR was not efficacious in obtaining and maintaining an adequate VDTL in this nursing home resident population.

CLINICAL TRIALS REGISTRATION NUMBER

NTR6029 (The Netherlands National Trial Register).

MANAGEMENT OF ENDOCRINE DISEASE: Therapeutics of Vitamin D

OBJECTIVE

The central role of vitamin D in bone health is well recognized. However, controversies regarding its clinical application remain. We therefore aimed to review the definition of hypovitaminosis D, the skeletal and extra-skeletal effects of vitamin D and the available therapeutic modalities.

DESIGN

Narrative and systematic literature review.

METHODS

An international working group that reviewed the current evidence linking bone and extra-skeletal health and vitamin D therapy to identify knowledge gaps for future research.

RESULTS

Findings from observational studies and randomized controlled trials (RCTs) in vitamin D deficiency are discordant, with findings of RCTs being largely negative. This may be due to reverse causality with the illness itself contributing to low vitamin D levels. The results of many RCTs have also been inconsistent. However, overall evidence from RCTs shows vitamin D reduces fractures (when administered with calcium) in the institutionalized elderly. Although controversial, vitamin D reduces acute respiratory tract infections (if not given as bolus monthly or annual doses) and may reduce falls in those with the lowest serum 25-hydroxyvitamin D (25OHD) levels. However, despite large ongoing RCTs with 21 000–26 000 participants not recruiting based on baseline 25OHD levels, they will contain a large subset of participants with vitamin D deficiency and are adequately powered to meet their primary end-points.

CONCLUSIONS

The effects of long-term vitamin D supplementation on non-skeletal outcomes, such as type 2 diabetes mellitus (T2DM), cancer and cardiovascular disease (CVD) and the optimal dose and serum 25OHD level that balances extra-skeletal benefits (T2DM) vs risks (e.g. CVD), may soon be determined by data from large RCTs.

Global prevalence and disease burden of vitamin D deficiency: a roadmap for action in low- and middle-income countries

Vitamin D is an essential nutrient for bone health and may influence the risks of respiratory illness, adverse pregnancy outcomes, and chronic diseases of adulthood. Because many countries have a relatively low supply of foods rich in vitamin D and inadequate exposure to natural ultraviolet B (UVB) radiation from sunlight, an important proportion of the global population is at risk of vitamin D deficiency. There is general agreement that the minimum serum/plasma 25-hydroxyvitamin D concentration (25(OH)D) that protects against vitamin D deficiency-related bone disease is approximately 30 nmol/L; therefore, this threshold is suitable to define vitamin D deficiency in population surveys. However, efforts to assess the vitamin D status of populations in low- and middle-income countries have been hampered by limited availability of population-representative 25(OH)D data, particularly among population subgroups most vulnerable to the skeletal and potential extraskeletal consequences of low vitamin D status, namely exclusively breastfed infants, children, adolescents, pregnant and lactating women, and the elderly. In the absence of 25(OH)D data, identification of communities that would benefit from public health interventions to improve vitamin D status may require proxy indicators of the population risk of vitamin D deficiency, such as the prevalence of rickets or metrics of usual UVB exposure. If a high prevalence of vitamin D deficiency is identified (>20% prevalence of 25(OH)D < 30 nmol/L) or the risk for vitamin D deficiency is determined to be high based on proxy indicators (e.g., prevalence of rickets >1%), food fortification and/or targeted vitamin D supplementation policies can be implemented to reduce the burden of vitamin D deficiency-related conditions in vulnerable populations.

Can adverse effects of excessive vitamin D supplementation occur without developing hypervitaminosis D?

Vitamin D is a fat-soluble hormone that has endocrine, paracrine and autocrine functions. Consumption of vitamin D-supplemented food & drugs have increased significantly in the last couple of decades due to campaign and awareness programs. Despite such wide use of artificial vitamin D supplements, serum level of 25 hydroxyvitamin D does not always reflect the amount of uptake. In contrast to the safe sunlight exposure, prolonged and disproportionate consumption of vitamin D supplements may lead to vitamin D intoxication, even without developing hypervitaminosis D. One of the reasons why vitamin D supplementation is believed to be safe is, it rarely raises serum vitamin D levels to the toxic range even after repeated intravenous ingestion of extremely high doses of synthetic vitamin D analogs. However, prolonged consumption of vitamin D supplementation may induce hypercalcemia, hypercalciuria and hyperphosphatemia, which are considered to be the initial signs of vitamin D intoxication. It is likely that calcium and phosphorus dysregulation, induced by exogenous vitamin D supplementation, may lead to tissue and organ damages, even without developing hypervitaminosis D. It is needed to be emphasized that, because of tight homeostatic control of calcium and phosphorus, when hypercalcemia and/or hyperphosphatemia is apparent following vitamin D supplementation, the process of tissue and/or organ damage might already have been started.

Vitamin D-Mediated Hypercalcemia: Mechanisms, Diagnosis, and Treatment

Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH)₂D], and impaired degradation of 1,25(OH)₂D. The ingestion of excessive amounts of vitamin D₃ (or vitamin D₂) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH)₂D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH)₂D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH)₂D is impaired as a result of mutations of the 1,25(OH)₂D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)₂D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH)₂D and evidence of impaired 24-hydroxylase-mediated 1,25(OH)₂D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.

Vitamin D in corticosteroid-naïve and corticosteroid-treated Duchenne muscular dystrophy: what dose achieves optimal 25(OH) vitamin D levels?

AIM

Assessment of the efficacy of vitamin D replenishment and maintenance doses required to attain optimal levels in boys with Duchenne muscular dystrophy (DMD).

METHOD

25(OH)-vitamin D levels and concurrent vitamin D dosage were collected from retrospective case-note review of boys with DMD at the Dubowitz Neuromuscular Centre. Vitamin D levels were stratified as deficient at <25 nmol/L, insufficient at 25-49 nmol/L, adequate at 50-75 nmol/L and optimal at >75 nmol/L.

RESULT

617 vitamin D samples were available from 197 boys (range 2-18 years)-69% from individuals on corticosteroids. Vitamin D-naïve boys (154 samples) showed deficiency in 28%, insufficiency in 42%, adequate levels in 24% and optimal levels in 6%. The vitamin D-supplemented group (463 samples) was tested while on different maintenance/replenishment doses. Three-month replenishment of daily 3000 IU (23 samples) or 6000 IU (37 samples) achieved optimal levels in 52% and 84%, respectively. 182 samples taken on 400 IU revealed deficiency in 19 (10%), insufficiency in 84 (47%), adequate levels in 67 (37%) and optimal levels in 11 (6%). 97 samples taken on 800 IU showed deficiency in 2 (2%), insufficiency in 17 (17%), adequate levels in 56 (58%) and optimal levels in 22 (23%). 81 samples were on 1000 IU and 14 samples on 1500 IU, with optimal levels in 35 (43%) and 9 (64%), respectively. No toxic level was seen (highest level 230 nmol/L).

CONCLUSIONS

The prevalence of vitamin D deficiency and insufficiency in DMD is high. A 2-month replenishment regimen of 6000 IU and maintenance regimen of 1000-1500 IU/day was associated with optimal vitamin D levels. These data have important implications for optimising vitamin D dosing in DMD.

Efficacy and safety of pamidronate in children with vitamin D intoxication

BACKGROUND

Bisphosphonates are used in the treatment of vitamin D intoxication (VDI) after failure of conventional therapy including prednisolone. Safety concerns restrict the use of bisphosphonates from being used as first-line therapy for VDI in children. The aim of this study was to evaluate the efficacy and safety of pamidronate in comparison with prednisolone in children with VDI.

METHODS

We reviewed the hospital records of children consecutively diagnosed with VDI at two medical centers in a 15 year period.

RESULTS

The subjects consisted of 21 children (age, 0.3-4.2 years) who were treated with prednisolone and/or bisphosphonates. Pamidronate (n = 18) or alendronate (n = 3) was used in six patients after unsuccessful prednisolone treatment, and in 15 patients from baseline. Initial serum calcium and 25-hydroxyvitamin D were 16.1 ± 1.9 mg/dL and 493 ± 219 ng/mL, respectively. The median time to reach normocalcemia in the pamidronate, alendronate and prednisolone groups was 3 days (range, 2-12 days), 4 days (range, 3-6 days) and 17 days (range, 12-26 days), respectively (P = 0.013). The pamidronate group had a fivefold shorter hospital stay than the prednisolone group. Three patients initially treated with prednisolone developed nephrocalcinosis but this did not occur in any patient treated with bisphosphonates from baseline. Apart from transient fever and moderate hypophosphatemia, no side-effect of bisphosphonate treatment was observed.

CONCLUSIONS

Pamidronate is efficient and safe for the treatment of VDI in children. Pamidronate use significantly shortens the duration of treatment, and thereby may prevent the development of nephrocalcinosis. Instead of prednisolone, pamidronate should be used together with hydration and furosemide as the first-line therapy for VDI.

Excess 25-hydroxyvitamin D3 exacerbates tubulointerstitial injury in mice by modulating macrophage phenotype

Vitamin D hydroxylated at carbon 25 (25(OH)D) is generally recognized as a precursor of active vitamin D. Despite its low affinity for the vitamin D receptor (VDR), both deficient and excessive 25(OH)D levels are associated with poor clinical outcomes. Here we studied direct effects of 25(OH)D3 on the kidney using 25(OH)D-1α-hydroxylase (CYP27B1) knockout mice. The effects of 25(OH)D3 on unilateral ureteral obstruction were analyzed as proximal tubular cells and macrophages are two major cell types that take up 25(OH)D and contribute to the pathogenesis of kidney injury. Excess 25(OH)D3 in obstructed mice worsened oxidative stress and tubulointerstitial fibrosis, whereas moderate levels of 25(OH)D3 had no effects. The exacerbating effects of excess 25(OH)D3 were abolished in CYP27B1/VDR double-knockout mice and in macrophage-depleted CYP27B1 knockout mice. Excess 25(OH)D3 upregulated both M1 marker (TNF-α) and M2 marker (TGF-β1) levels of kidney-infiltrating macrophages. In vitro analyses verified that excess 25(OH)D3 directly upregulated TNF-α and TGF-β1 in cultured macrophages but not in tubular cells. TNF-α and 25(OH)D3 cooperatively induced oxidative stress by upregulating iNOS in tubular cells. Aggravated tubulointerstitial fibrosis in mice with excess 25(OH)D3 indicated that macrophage-derived TGF-β1 also had a key role in the pathogenesis of surplus 25(OH)D3. Thus, excess 25(OH)D3 worsens tubulointerstitial injury by modulating macrophage phenotype.

Iatrogenic vitamin D toxicity in an infant--a case report and review of literature

Public concern over vitamin D deficiency has led to widespread use of over the counter (OTC) vitamin D (-D3 or -D2) supplements, containing up to 10,000 IU/unit dose (400 IU=10μg). Overzealous use of such supplements can cause hypercalcemia due to vitamin D toxicity. Infants are particularly vulnerable to toxicity associated with vitamin D overdose. OTC supplements are not subject to stringent quality control regulations from FDA and high degree of variability in vitamin D content in OTC pills has been demonstrated. Other etiologies of vitamin D induced hypercalcemia include hyperparathyroidism, granulomatous malignancies like sarcoidosis and mutations in the CYP24A1 gene. The differential diagnosis of hypercalcemia should include iatrogenic and genetic etiologies. C24-hydroxylation and C3-epimerization are two important biochemical pathways via which 25-hydroxyvitamin D3 (25(OH)D3) is converted to its metabolites, 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) or its C3 epimer, 3-epi-25-OH-D3 respectively. Mutations in the CYP24A1 gene cause reduced serum 24,25(OH)2D3 to 25(OH)D3 ratio (<0.02), elevated serum 1,25-dihydroxyvitamin D (1,25(OH)2D3), hypercalcemia, hypercalciuria and nephrolithiasis. Studies in infants have shown that 3-epi-25(OH)D3 can contribute 9-61.1% of the total 25(OH)D3. Therefore, measurements of parathyroid hormone (PTH) and vitamin D metabolites 25(OH)D3, 1,25(OH)2D3, 3-epi-25(OH)D3 and 24,25(OH)2D3 are useful to investigate whether the underlying cause of vitamin D toxicity is iatrogenic versus genetic. Here we report a case of vitamin D3 associated toxicity in a 4-month-old female who was exclusively breast-fed and received an oral liquid vitamin D3 supplement at a dose significantly higher than recommended on the label. The vitamin D3 content of the supplement was threefold higher (6000 IU of D/drop) than listed on the label (2000 IU). Due to overdosing and higher vitamin D3 content, the infant received ∼50,000 IU/day for two months resulting in severe hypercalcemia, hypercalciuria and nephrocalcinosis. We also review the relevant literature on vitamin D3 toxicity in this report.

Hypercalcemia in the Intensive Care Unit: A Review of Pathophysiology, Diagnosis, and Modern Therapy

Hypercalcemia may be seen in a variety of clinical settings and often requires intensive management when serum calcium levels are dramatically elevated. All of the many etiologies of mild hypercalcemia can lead to severe hypercalcemia. Knowledge of the physiologic mechanisms involved in maintaining normocalcemia and basic pathophysiology is essential for making a timely diagnosis and hence prompt institution of etiology-specific therapy. The development of new medications and critical reviews of traditional therapies have changed the treatment paradigm for severe hypercalcemia, calling for a more limited role for aggressive isotonic fluid administration and furosemide and an expanded role for calcitonin and the bisphosphonates. Experimental therapies such as denosumab show promise.

Vitamin D: deficiency, sufficiency and toxicity

The plethora of vitamin D studies over the recent years highlight the pleomorphic effects of vitamin D outside its conventional role in calcium and bone homeostasis. Vitamin D deficiency, though common and known, still faces several challenges among the medical community in terms of proper diagnosis and correction. In this review, the different levels of vitamin D and its clinical implications are highlighted. Recommendations and consensuses for the appropriate dose and duration for each vitamin D status are also emphasized.

Comparison of oral alendronate versus prednisolone in treatment of infants with vitamin D intoxication

AIM

The aim of this report was to compare the efficacy of oral alendronate versus prednisolone treatment in addition to conventional measures in infants with vitamin D intoxication.

METHODS

In six infants (aged 8.0 ± 2.1 months) with vitamin D intoxication, time to achieve normocalcemia with prednisolone treatment (Group I, n = 4) or alendronate treatment (Group II, n = 4, two infants started treatment from the baseline and two after unsuccessful prednisolone treatment) in addition to intravenous hydration and diuretic therapy were compared.

RESULTS

Baseline serum calcium levels ranged between 3.8 and 4.77 mmol/L. In the prednisolone group, although two patients reached normocalcemia on 7th and 12th days of treatment, other two patients did not despite 23 and 15 days of treatment and therefore switched to alendronate treatment. The mean duration of prednisolone treatment in these four patients was 14.2 ± 6.7 days (range 7-23). In the alendronate group, two patients who started treatment from the baseline achieved normocalcemia on the 5th day. Other two patients achieved normocalcemia 2 days after switching to alendronate. Thus, the mean time to reach normocalcemia after single oral alendronate administration was 3.5 ± 1.7 days (range 2-5) (p < 0.01 versus Group I).

CONCLUSION

Alendronate treatment achieves normocalcemia four times earlier than prednisolone treatment and shortens hospital stay in infants with vitamin D intoxication.

Dihydrotachysterol intoxication treated with pamidronate: a case report

Introduction

Hypoparathyroidism is a chronic condition which requires a lifelong substitution with vitamin D analogues and careful monitoring. This is especially true for older patients and older compounds as dihydrotachysterol with longer half-life that might lead to long-lasting hypercalcemic episodes.

Case presentation

A 74-year old male patient with postsurgical hypoparathyroidism who has been successfully supplemented with dihydrotachysterol (1.7 ml/day) for over 50 years presented with neuropsychiatric disturbances, constipation, renal insufficiency and polyuria. Laboratory investigation demonstrated serum calcium 3.7 mmol/L, serum creatinine 180 micromol/L, urine calcium excretion 1.1 mmol/mmol of the creatinine, normal 25 OH vitamin D₃ and low parathormone and 1,25 di OH vitamin D₃. Careful history revealed that he has been erroneously taking 2.5 ml of dihydrotachysterol per day for at least 6 to 8 weeks that caused vitamin D intoxication and symptomatic hypercalcemia. He was treated with intravenous saline infusion, prednisolone and 60 mg of intravenous sodium pamidronate. On the fourth day after admission serum calcium dropped rapidly within the reference range. The treatment for hypoparathyroidism had to be reinstituted 10 days after dihydrotachysterol had been discontinued when the patient was switched to shorter acting calcitriol.

Conclusions

Here we reported that the immediate use of pamidronate in addition to classic treatment of dihydrotachysterol intoxication with intravenous saline, diuretics and glucocorticoids is an effective treatment choice that leads to rapid resolution of hypercalcemia.

Pharmacokinetics of vitamin D toxicity

Although researchers first identified the fat-soluble vitamin cholecalciferol almost a century ago and studies have now largely elucidated the transcriptional mechanism of action of its hormonal form, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], we know surprisingly little about mechanisms of vitamin D toxicity. The lipophilic nature of vitamin D explains its adipose tissue distribution and its slow turnover in the body (half-life approximately 2 mo). Its main transported metabolite, 25-hydroxyvitamin D(3) [25(OH)D(3)], shows a half-life of approximately 15 d and circulates at a concentration of 25-200 nmol/L, whereas the hormone 1alpha,25(OH)(2)D(3) has a half-life of approximately 15 h. Animal experiments involving vitamin D(3) intoxication have established that 25(OH)D(3) can reach concentrations up to 2.5 mumol/L, at which it is accompanied by hypercalcemia and other pathological sequelae resulting from a high Ca/PO(4) product. The rise in 25(OH)D(3) is accompanied by elevations of its precursor, vitamin D(3), as well as by rises in many of its dihydroxy- metabolites [24,25(OH)(2)D(3); 25,26(OH)(2)D(3); and 25(OH)D(3)-26,23-lactone] but not 1alpha,25(OH)(2)D(3). Early assumptions that 1alpha,25(OH)(2)D(3) might cause hypercalcemia in vitamin D toxicity have been replaced by the theories that 25(OH)D(3) at pharmacologic concentrations can overcome vitamin D receptor affinity disadvantages to directly stimulate transcription or that total vitamin D metabolite concentrations displace 1alpha,25(OH)(2)D from vitamin D binding, increasing its free concentration and thus increasing gene transcription. Occasional anecdotal reports from humans intoxicated with vitamin D appear to support the latter mechanism. Although current data support the viewpoint that the biomarker plasma 25(OH)D concentration must rise above 750 nmol/L to produce vitamin D toxicity, the more prudent upper limit of 250 nmol/L might be retained to ensure a wide safety margin.

Pamidronate treatment of hypercalcemia caused by vitamin D toxicity

We present a 16 month-old previously healthy boy with refractory hypercalcemia due to an overdose of an over-the-counter vitamin supplement. The patient presented to the emergency department with a few weeks' history of irritability, constipation and intermittent vomiting. His serum calcium was found to be 18 mg/dl. He was first treated with intravenous fluids, furosemide and glucocorticoids without significant improvement, but became eucalcemic within 24 hours after receiving a single dose of pamidronate. This case highlights the potential danger of high dose vitamin supplements in children, and the salutary effects of treatment with bisphosphonate.

Safety of vitamin D3 in adults with multiple sclerosis

BACKGROUND

Vitamin D3 may have therapeutic potential in several diseases, including multiple sclerosis. High doses of vitamin D(3) may be required for therapeutic efficacy, and yet tolerability--in the present context, defined as the serum concentration of 25-hydroxyvitamin D [25(OH)D] that does not cause hypercalcemia--remains poorly characterized.

OBJECTIVE

The objective of the study was to characterize the calcemic response to specific serum 25(OH)D concentrations.

DESIGN

In a 28-wk protocol, 12 patients in an active phase of multiple sclerosis were given 1200 mg elemental Ca/d along with progressively increasing doses of vitamin D3: from 700 to 7000 microg/wk (from 28 000 to 280 000 IU/wk).

RESULTS

Mean (+/- SD) serum concentrations of 25(OH)D initially were 78 +/- 35 nmol/L and rose to 386 +/- 157 nmol/L (P < 0.001). Serum calcium concentrations and the urinary ratio of calcium to creatinine neither increased in mean values nor exceeded reference values for any participant (2.1-2.6 mmol/L and <1.0, respectively). Liver enzymes, serum creatinine, electrolytes, serum protein, and parathyroid hormone did not change according to Bonferroni repeated-measures statistics, although parathyroid hormone did decline significantly according to the paired t test. Disease progression and activity were not affected, but the number of gadolinium-enhancing lesions per patient (assessed with a nuclear magnetic brain scan) decreased from the initial mean of 1.75 to the end-of-study mean of 0.83 (P = 0.03).

CONCLUSIONS

Patients' serum 25(OH)D concentrations reached twice the top of the physiologic range without eliciting hypercalcemia or hypercalciuria. The data support the feasibility of pharmacologic doses of vitamin D3 for clinical research, and they provide objective evidence that vitamin D intake beyond the current upper limit is safe by a large margin.

Risk assessment for vitamin D

The objective of this review was to apply the risk assessment methodology used by the Food and Nutrition Board (FNB) to derive a revised safe Tolerable Upper Intake Level (UL) for vitamin D. New data continue to emerge regarding the health benefits of vitamin D beyond its role in bone. The intakes associated with those benefits suggest a need for levels of supplementation, food fortification, or both that are higher than current levels. A prevailing concern exists, however, regarding the potential for toxicity related to excessive vitamin D intakes. The UL established by the FNB for vitamin D (50 microg, or 2000 IU) is not based on current evidence and is viewed by many as being too restrictive, thus curtailing research, commercial development, and optimization of nutritional policy. Human clinical trial data published subsequent to the establishment of the FNB vitamin D UL published in 1997 support a significantly higher UL. We present a risk assessment based on relevant, well-designed human clinical trials of vitamin D. Collectively, the absence of toxicity in trials conducted in healthy adults that used vitamin D dose > or = 250 microg/d (10,000 IU vitamin D3) supports the confident selection of this value as the UL.

Report on the vitamin D status of adult and pediatric patients with inflammatory bowel disease and its significance for bone health and disease

Vitamin D is a hormone responsible for calcium homeostasis and essential for bone mineralization throughout the lifespan. Recent studies revealed a high prevalence of hypovitaminosis D among healthy adults and children, especially in the northern hemisphere, and a link between this condition and suboptimal bone health. Moreover, maintenance of what are today considered optimal vitamin D stores has not been achieved throughout the year with currently recommended daily intake for vitamin D. The prevalence of hypovitaminosis D is even higher among adults with inflammatory bowel disease (IBD), a situation that may be caused by malabsorption and gastrointestinal losses through an inflamed intestine, among other factors. In children with IBD, existing reports of vitamin D status are scarce. The relationship between vitamin D status and bone health, although well-established in healthy adults and children, has been controversial among adults and children with IBD, and the reasons for this have not been investigated to date. Studies in animal models of colitis and in vitro human studies support a role of vitamin D in the regulation of the immune system of the gut and the potential of vitamin D and its derivatives as therapeutic adjuncts in the treatment of IBD. This role of vitamin D has not been investigated with translational studies to date. Currently, there are no guidelines for monitoring vitamin D status, treating hypovitaminosis D, and maintaining optimal vitamin D stores in patients with IBD. These tasks may prove particularly difficult because of malabsorption and gastrointestinal losses that are associated with IBD.

Critique of the considerations for establishing the tolerable upper intake level for vitamin D: critical need for revision upwards

The tolerable upper intake level (UL) for vitamin D is 50 mcg/d (2000 iu/d) in North America and in Europe. In the United Kingdom a guidance level exists for vitamin D, 25 mcg/d (1000 iu/d), defined as the dose "of vitamins and minerals that potentially susceptible individuals could take daily on a life-long basis, without medical supervision in reasonable safety." Exposure of skin to sunshine can safely provide an adult with vitamin D in an amount equivalent to an oral dose of 250 mcg/d. The incremental consumption of 1 mcg/d of vitamin D3 raises serum 25-hydroxyvitamin D [25(OH)D ] by approximately 1 nmol/L (0.4 microg/L). Published reports suggest toxicity may occur with 25(OH)D concentrations beyond 500 nmol/L (200 microg/L). Older adults are advised to maintain serum 25(OH)D concentrations >75 nmol/L. The preceding numbers indicate that vitamin D3 intake at the UL raises 25(OH)D by approximately 50 nmol/L and that this may be more desirable than harmful. The past decade has produced separate North American, European, and U.K. reports that address UL or guidance-level values for vitamin D. Despite similar well-defined models for risk assessment, each report has failed to adapt its message to new evidence of no adverse effects at higher doses. Inappropriately low UL values, or guidance values, for vitamin D have hindered objective clinical research on vitamin D nutrition, they have hindered our understanding of its role in disease prevention, and restricted the amount of vitamin D in multivitamins and foods to doses too low to benefit public health.

Vitamin D in foods and as supplements

Numerous studies have shown that the vitamin D status is far from optimal in many countries all over the world. The main reason for this is lack of sunshine. Only a limited number of foods naturally contain vitamin D. Good sources of vitamin D(3) are fish (not only fatty fish), egg yolk, and offal such as liver. Some foods such as milk are fortified with vitamin D in some countries. Dietary vitamin D intake is low in many countries, especially as the dietary sources are limited. The use of supplements is important and seems to be high in some countries. Current dietary intake recommendations are too low to preserve/reach optimal S-25-OHD concentrations, when UVB radiation is not available. We suggest that the recommendations should be increased to at least 10 microg per day in all age groups when solar UVB is scarce. The elderly may need a daily vitamin D intake of 25 microg. If dietary intake of vitamin D is to be increased, food habits will have to change. From a public health point of view it is better to increase the potential sources of vitamin D by fortifying specific products that are consumed commonly in a whole population, or if necessary by especially vulnerable groups. Supplement use is probably the right alternative for vulnerable groups such as infants and inactive elderly in whom this is more easily implemented.

Antiproliferative role of vitamin D and its analogs--a brief overview

The active metabolite of vitamin D, 1alpha, 25-dihydroxyvitamin D3 [1,25(OH)2D3]--a seco-steroid hormone is a pivotal regulator of cellular proliferation and differentiation those are independent of its classical function of calcium homeostasis and bone mineralization. The existence of the nuclear vitamin D receptor (VDR) has been found in numerous tissues in different organs, which are the so-called 'non-classical' targets of this seco-steroid hormone. Vitamin D has been documented as a potent antiproliferative agent in different tissues and cells. Epidemiological studies reveal a negative correlation between physiological level of vitamin and cancer risk. Studies using animal models clearly demonstrate protective role of vitamin D in different cancer types by the reduction in tumor progression and by monitoring biochemical parameters. Experiments with cultured human and animal cancer cell lines show similar antiproliferative role of vitamin D manifested by up or down regulations of crucial genes leading to inhibition of cellular growth. Hypercalcemia hinders broad-spectrum therapeutic uses of vitamin D in cancer chemotherapy. Application of vitamin D analogs having similar chemical structures or other compounds having vitamin D like actions but lacking calcemic adverse effects are getting significant attention towards rational therapeutics to treat cancer. The current review focuses on the application of vitamin D and its analogs in different forms of cancer and on the molecular mechanism involved in vitamin D mediated inhibition in cellular proliferation, cell cycle, induction of apoptosis and tumor suppression, which may eventually evolve as a meaningful cancer therapy.

Pamidronate treatment in acute vitamin D intoxication

Management with glucocorticoid, high iv fluid saline intake, furosemide and calcitonin may not result in a favorable reduction of hypercalcemia and may cause several side effects in infants with acute vitamin D intoxication. The bisphosphonate pamidronate, a specific inhibitor of bone resorption through osteoclast mediation was successfully used in a 6-month old infant with acute vitamin D intoxication managed in the Pediatric Emergency and Intensive Care Unit, after an ineffective trial of hydration, furosemide, calcitonin and prednisolone. After a double infusion of pamidronate on two consecutive days (1 mg/kg/day), an early and safe correction of hypercalcemia/hypercalciuria was supplied. Pamidronate therapy may be considered in patients with hypercalcemia secondary to acute vitamin D poisoning.

Oral bisphosphonate therapy for vitamin D intoxication of the infant

Vitamin D intoxication in infancy has serious consequences attributable to acute hypercalcemia and subsequent hypercalcuria/nephrocalcinosis. Current treatments of patients with vitamin D intoxication are unsatisfactory and associated with prolonged hypercalcemia. We now report the use of oral alendronate sodium in a 3-month-old infant with vitamin D intoxication. Short-term oral alendronate sodium treatment effectively corrected hypercalcemia/hypercalciuria, decreased the duration of hospitalization, and appears safe in 15 months of observation.

Lessons to be learned: a case study approach. Sunshine-induced hypercalcaemia?

A man of 56 years presented with severe hypercalcaemia shortly after returning from a holiday in the sun. The final diagnosis was sarcoidosis. Measurement of the metabolites of vitamin D did not support sunshine exposure as being a contributory factor to the hypercalcaemia. The effects of sarcoid tissue on calcium metabolism are discussed.

Pharmacotherapy of osteoporosis in postmenopausal women: focus on safety

The therapy of osteoporosis has made enormous strides in the last decade. There is now a range of interventions, each with its pros and cons. Calcium and vitamin D supplementation remain the foundation and have few safety issues. Bisphosphonates are widely used, though gastrointestinal tolerance is a problem with some oral preparations. Intravenous administration may circumvent this, although this introduces the smaller problem of acute phase reactions. The side effect profile of hormone replacement therapy (HRT) is still being delineated after 40 years of use, with substantial new information expected in the next few years. This will clarify its place in the medical management of the menopause. Raloxifene appears to have a superior safety profile to HRT, though its efficacy on bone may be less. While none of these options is suitable for everyone, the range of available therapies does mean that most patients can find an intervention that is effective and acceptable.

Vitamin D and genomic stability

1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] has been shown to act on novel target tissues not related to calcium homeostasis. There have been reports characterizing 1,25(OH)(2)D(3) receptors and activities in diverse tissues such as brain, pancreas, pituitary, skin, muscle, placenta, immune cells and parathyroid. The receptor hormone complex becomes localized in the nucleus, and undergoes phosphorylation by reacting with a kinase. This form of the receptor then interacts with the Vitamin D responsive element of target gene and modifies the transcription of those genes to develop the action. The modulation of gene transcription results in either the induction or repression of specific messenger RNAs (m-RNAs), ultimately resulting in changes in protein expression needed to produce biological responses. Genes for carbonic anhydrase that are expressed at high levels in osteoclast are known to be involved in bone resorption and Id genes role in osteoblast-osteoclast differentiation reflects the genomic effect of Vitamin D on bones. Genomic action of Vitamin D also explains the biosynthesis of oncogenes, polyamines, lymphokines and calcium binding proteins. However, there is a possibility that some of the actions of 1,25(OH)(2)D(3) may be mediated by non-genomic mechanisms and may not require the binding to Vitamin D receptor (VDR). Vitamin D offers a protection from genotoxic effects of Vitamin D deficiency by increasing the insulin receptor gene expression and BSP (bone sialoprotein), bone-remodeling by decreasing the osteopontin (OPN) m-RNAs, maintaining the normal epidermal structure and enamel matrix. Gonadal insufficiency in Vitamin D deficiency was corrected by vitamin mediated direct regulation of the expression of aramotase gene. The supportive role of Vitamin D in placental function is also evident by its influence on human placental lactogen (hpl) gene transcription accompanied by increase hpl m-RNA levels. Further role of Vitamin D is envisaged in identifying cyclin C as an important target for Vitamin D in cell-cycle regulation. Vitamin D at physiological concentration has been found to protect cell proteins and membranes against oxidative stress by inhibiting the peroxidative attack on membrane lipids. Vitamin D, at a concentration range of 2x10(-8)-5x10(-8)M, induces apoptosis in most cancer cells, stabilizes chromosomal structure and prevents DNA double-strand breaks induced either by endogenous or exogenous factors. Vitamin D is also effective in stimulating DNA synthesis in adult alveolar II cells and provides a novel mechanism of modulation of epithelial cell proliferation in the context of lung development and repair against injury. The regulation of various proto-oncogenes (c-myc, c-fos, c-jun), differentiation inducing properties, antiproliferative effects on keratinocytes and inhibitory effects in several human malignancy ranks Vitamin D as a novel hormone that may have physiological and clinical implication in the carcinogenic process.

Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety

For adults, the 5-microg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension. Total-body sun exposure easily provides the equivalent of 250 microg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit. Sailors in US submarines are deprived of environmentally acquired vitamin D equivalent to 20-50 microg (800-2000 IU)/d. The assembled data from many vitamin D supplementation studies reveal a curve for vitamin D dose versus serum 25-hydroxyvitamin D [25(OH)D] response that is surprisingly flat up to 250 microg (10000 IU) vitamin D/d. To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 microg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 microg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of > or = 1000 microg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 microg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 microg (2000 IU)/d is too low by at least 5-fold.

The use of pamidronate for hypercalcemia secondary to acute vitamin D intoxication

INTRODUCTION

Pamidronate disodium, a bone resorption inhibitor through osteoclast mediation, has been used to treat chronic hypercalcemia secondary to malignancy and chronic renal failure. We report the use of pamidronate for acute, severe hypercalcemia secondary to iatrogenic vitamin D poisoning.

CASE REPORT

A 77-year-old female nursing home resident was inadvertently administered 50,000 units of oral vitamin D daily for 6 days. The patient presented with lethargy, abdominal pain, and vomiting. The patient's initial serum calcium concentration was 5.25 mmol/L (21 mg/dL). The patient was initially treated with hydration and furosemide but developed congestive heart failure. Pamidronate was used and calcium concentrations normalized by 24 hours after treatment.

CONCLUSION

We report a case of the use of pamidronate for significant hypercalcemia secondary to acute vitamin D poisoning. Although evidence of congestive heart failure was evident, dialysis was avoided without significant sequelae. Pamidronate therapy should be considered in patients with hypercalcemia secondary to acute vitamin D poisoning.

Bisphosphonate therapy

The bisphosphonates are long-lived synthetic analogs of pyrophosphate, a natural, short-lived inhibitor of bone. Oral doses share similar qualities (ie, they inhibit bone resorption, poor absorption, and potential gastrointestinal irritants), but each one has a unique spectrum of potency and a probable mechanism of action. The parent compound, etidronate, was first used in multicentered trials for the treatment of primary osteoporosis and showed some success in increasing bone density and perhaps controlling fracture rates. The recently approved drug alendronate is a more potent agent than etidronate, produces a greater increase in bone density, and decreases fractures. Oral and intravenous pamidronate have similar positive effects on bone density. Studies with tiludronate, risedronate, and clodronate show similar promise as therapeutic agents.

In vitro inhibition of membrane-mediated calcification by novel phosphonates

The effects of a series of novel phosphonates on the kinetics of mineral development in an ionophore-primed 7:2:1 phosphatidylcholine (PC): dicetylphosphate (DCP): cholesterol (Chol) liposomal model system are reported. When present at 2.5 micromol/liter or 25 micromol/liter concentrations in the solution surrounding the liposomes, the investigated phosphonates did not significantly delay the initial formation of hydroxyapatite-like calcium phosphate salts (HAP) within the liposomes or the penetration of HAP crystals through the enclosing membranes. However, the phosphonates variably retarded the subsequent growth and proliferation of the HAP crystals once they became directly exposed to the phosphonate-containing solution. The effectiveness of phosphonates in inhibiting extraliposomal precipitation strongly depended on their structure. The inhibitory action on active surface growth sites of released intraliposomal crystals was found to be the most effective if the phosphonate molecule contained two phosphonic groups linked to the same C atom. At a phosphonate concentration of 25 micromol/liter, the following general order of effectiveness was established: geminal bisphosphonate >/= geminal tetrakisphosphonate > bisacylphosphonates > monoacylphosphonate > bisalkylphosphonate. Within the bisacylphosphonate family, the highest inhibitory action was observed when four or five -CH2- groups separated the ketophosphonic groups.

Vitamin D intoxication causes hypercalcaemia by increased bone resorption which responds to pamidronate

OBJECTIVE

Vitamin D intoxication is a relatively rare but treatable cause of hypercalcaemia. In the past this has been undertaken using corticosteroids. Previous observations have suggested that there is increased bone resorption in hypervitaminosis D. If this were to be the case, specific inhibitors of bone resorption might provide more effective treatment. We have therefore studied the mechanisms of hypercalcaemia and response to therapy in a group of patients with vitamin D intoxication.

DESIGN

Vitamin D metabolites were measured in six patients with vitamin D intoxication; in five of these the components of hypercalcaemia were calculated. These measurements were repeated following treatment with corticosteroids (two patients) or the bisphosphonate, pamidronate (three patients).

RESULTS

In each case the serum 25-hydroxyvitamin D was grossly elevated and there was a more modest elevation in serum 1,25-dihydroxyvitamin D. The components of hypercalcaemia suggest that there was a significant degree of bone resorption in all six patients and that this is the major determinant of hypercalcaemia. Pamidronate treatment resulted in a brisk reduction in plasma calcium concentration. Following corticosteroids the return of calcium to normal was more delayed.

CONCLUSION

The hypercalcaemia of vitamin D intoxication is mediated by increased bone resorption and bisphosphonates have a role in its management.